Indexable inserts detachably mountable to tools for cutting workpieces have been known to date. Many proposals of such indexable inserts in which a hard coating film of a ceramic or the like is formed on a substrate composed of a cemented carbide or cermet to improve wear resistance and toughness have been made.
For such indexable inserts having the above-described structure, various attempts have been made, such as changing the composition of the hard coating film or changing the thickness of the hard coating film from a flank face to a rake face, to improve various characteristics (refer to Japanese Unexamined Patent Application Publication Nos. 2001-347403 (Patent Document 1), 2004-122263 (Patent Document 2), 2004-122264 (Patent Document 3), and 2004-216488 (Patent Document 4)).
However, although recent years saw increasing need for high-speed cutting and precision cutting, and high-efficiency cutting of difficult-to-cut materials, there have been developed no indexable insert that simultaneously achieves both high wear resistance and high toughness required for these types of cutting and that prevents separation of the surface layer.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-347403    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-122263    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2004-122264    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2004-216488